1. Field of the Invention
This invention concerns a method of forming a crystalline semiconductor thin film on a substrate, a lamination formed with a crystalline semiconductor thin film on a substrate, a lamination for use in a substrate provided with a transparent conductive thin film and a transparent semiconductor thin film used for production of various kinds of display devices such as CCD cameras or liquid crystal display devices or camera image sensors, particularly, for the color filter suitable to portable terminals such as portable telephones or small personal computers, as well as color filters manufactured by using the substrate.
2. Description of the Related Art
Photoconductors having catalytic activity or photovoltaic activity have been noted for their specific applications in recent years. For example, titanium dioxide as a photosemiconductor is said to oxidatively decompose organic contaminants deposited on the surface, air contaminating substances such as nitrogen oxides (NOx), sulfur oxides (SOx) and malodor substances, as well as bacteria by the oxidizing action based on the photocatalytic activity. As actual application examples, various uses have been proposed such as a method of appending a titanium dioxide photocatalyst on outer walls of buildings to elate air contaminating substances under sunlight. (Japanese Published Unexamined Patent Application No. Hei 6-315614). A method of appending a titanium dioxide catalyst on walls or hand rails in hospitals thereby killing bacteria (Japanese Published Unexamined Patent Application No. Hei 7-102678), a method of dispersing a powder of titanium dioxide catalyst in waste water and applying the light of a UV-ray lamp to decompose dirt in water (Japanese Published Unexamined Patent Application No. Hei 5-92192) or a method of utilizing a self-cleaning effect of a photocatalyst in order to mitigate cleaning maintenance for fluorescent lamps or illumination instruments (Japanese Published Unexamined Patent Application Hei 9-129012).
Further, it has been known that the surface of the photoconductive thin film is rendered a highly hydrophilic based on the photoreaction, and various application uses have been considered for preventing clouding of mirrors (in bath rooms or automobiles), lenses and glass windows.
It has also been known that a self-cleaning effect is obtained when the photosemiconductor thin film is formed on surfaces of building outer walls, automobile glass and window glass, hydrophobic dirt is less deposited and, in addition, dirt, if deposited, is decomposed based on the hydrophilic property on the surface of the film and the dirt or the decomposition products thereof are easily flushed away by rain fall or water washing due to the hydrophilic property of the photoconductor thin films.
For the preparation of photosemiconductor thin films, there have been known a method of hydrolyzing a titanium compound such as titanium alkoxide or titanium acetate, coating and drying the product on the surface of a base material and then sintering at a temperature of 500xc2x0 C. or higher thereby obtaining an anatase type titanium dioxide film, a method of forming an amorphous titanium dioxide layer by a vapor deposition process and annealing the resultant amorphous titanium dioxide layer at 400xc2x0 C. or higher to form a layer containing anatase type titanium dioxide, a method of crystallizing the surface of metal titanium by oxidizing at a temperature of 500xc2x0 C. or higher or a method of obtaining an anatase type titanium dioxide film by an RF sputtering method in a state of heating a base material to 250xc2x0 C. or higher.
In the methods described above, the method of forming a photosemiconductor thin film by sintering the amorphous titanium dioxide film requires heating of the substrate at a high temperature for a long time, which increases the cost in view of economy. Further, formation of the photoconductor thin film by this method on a plastic base material to be described later is actually impossible in view of the heat resistance of the plastic substrate. Further, while the RF sputtering method is excellent as a method of obtaining an anatase titanium dioxide of high photovoltaic activity, it is necessary to use an expensive apparatus and it is difficult to manufacture the photoconductor thin film at a reduced cost by this method. Although some of plastic base materials have heat resistance of 250xc2x0 C., those having heat resistance of 250xc2x0 C. and also having transparency and available at a reasonable cost have not yet been known at present.
By the way, the photoconductor thin film has been noted for the photovoltaic function in addition to characteristics such as antifouling, antibacterial and anti clouding effect based on the photochemical reaction on the surface as described above. The photovoltaic effect is a phenomenon that when a substrate provided with a conductive thin film and a photoconductor thin film is dipped in water or a solution having an electrolyzing function and UV-rays are applied to the photoconductor thin film, photovoltaic activity is generated at the irradiated area. By utilizing the phenomenon, a film can be formed selectively for example to the irradiated area. That is, when the substrate is dipped in an electrodeposition solution containing a film forming electrodeposition substance and UV-rays are applied to the photoconductive thin film in a state of applying or not applying a bias voltage between the conductive thin film and a counter electrode located in the solution, photovoltaic activity is generated at the light-irradiated area of the photosemiconductor thin film and the film forming substance is electrodeposited to the area. In the case where the photovoltaic activity of the semiconductor thin film is sufficiently large, the bias voltage can be reduced to 0.
The present inventors have previously filed a method of forming an extremely fine pattern at a good resolution which is useful for a color filter or the like by utilizing the photovoltaic activity (Japanese Published Unexamined Patent Application Nos. Hei 1-174790, Hei 11-133224, and Hei 11-335894).
In recent years, liquid crystal display panels provided with color filter include (1) those having a driving substrate on which driving elements such as thin film transistors (hereinafter sometimes referred to as xe2x80x9cTFTxe2x80x9d) and pixel electrodes are arranged in a matrix and a filter substrate having a color filter and a counter electrode which are opposed under positional alignment by way of a spacer in which a liquid crystal material is sealed in a gap portion and (2) those having a color filter-integrated type driving substrate with the color filter being formed directly to the driving substrate and a counter substrate having an electrode opposed to each other simply by way of a spacer in which liquid material is sealed in the gap portion. Each of the color filters described above can be manufactured by the photo-electrodeposition method using the photosemiconductor thin film as described in the patent publications.
The former liquid crystal display panel involves the problem in that an exposure mask is required upon manufacture of the color filter and error tends to occur in the accuracy of the positional alignment between both of the driving and filter substrates to lower the display quality or production yield. On the other hand, the latter has been noted at present since a bias voltage can be applied selectively by TFT disposed on the driving substrate (addressing), so that the exposure mask is not necessary and positional alignment is not required between both of the substrates the manufactured of the color filter. However, the latter method leads to increase cost since it is necessary to make the color filter conductive by using through holes or the like.
Further, in recent years, demand for smaller size equipment as portable terminals such as telephones or small personal computers has tended to increase rapidly and various studies have been made with a viewpoint of portable performance. Particularly, in the case of equipment with an aim of portable use, portability in outdoor and impact shock resistance to external force are considered important and it is demanded that they are light in weight and cause less breakage upon dropping or the like.
With the viewpoint, use of flexible plastic substrates has been noted instead of existent glass substrates as a substrate for constituting a liquid display panel. Generally, for the flexible substrates for the liquid crystal use, plastic materials having transparency and high heat resistance and excellent in gas barrier property have been demanded, but the heat resistance is only about at 223xc2x0 C. even in polyether sulfone (PES) which is considered to have the highest heat resistance, so that it is difficult to dispose the photosemiconductor thin film described above on the plastic substrate and formation of the color filter by the photo-electrodeposition method on the plastic substrate has not yet been attained commercially.
Further, for the liquid crystal panel using the plastic substrate, only the STN system not requiring TFT driving circuit has been known. This is because a high temperature processing step is necessary for forming a polycrystal semiconductor thin film at high carrier concentration used in TFT and manufacture of the TFT driving circuit on the plastic substrate is impossible at present. Then, as the method of manufacturing the color filter for use in the liquid crystal panel by adopting the plastic substrate, only (1) the ink jet method and (2) the electrodeposition method have been put to practical use. While the inkjet method has an advantage of not including a photolithographic step, it tends to cause color mixing and poor in view of the resolution and the positional accuracy. Further, since the electrodeposition method requires formation of an electrode corresponding to a pixel, the pattern shape is restricted to a stripe pattern or the like and cannot be used for the liquid crystal panel provided with a TFT driving circuit.
Further, manufacture of the TFT driving circuit to the plastic substrate is impossible at present as described above but there is a strong demand for the liquid crystal display panel using the plastic substrate provided with the TFT circuit. Particularly in recent years, there is a strong demand for the display capable of displaying video information and communication information at high resolution, and color filters of higher fineness has been demanded. For this purpose, it has been desired for the establishment in a method of manufacturing a flexible substrate provided with a TFT driving circuit capable of high fineness display and a method of forming a color filter to the substrate.
For this purpose, it has been demanded to manufacture not only the photosemiconductor thin film described above but also the semiconductor thin film such as used for the TFT circuit at a low temperature efficiently.
As a method of forming a semiconductor thin film on a plastic base material, Japanese Published Unexamined Patent Application No. Hei 6-11738 describes a method of manufacturing a semiconductive crystalline silicon film of an MIM device by irradiating the thin film surface of an insulative silicone-based compound material with an energy beam such as a laser beam thereby melting a surface layer and converting the surface layer to a crystalline silicon film while leaving the insulative silicon-based compound material to an under layer. Further, Unexamined Patent Application No. Hei 5-315361 discloses a method of manufacturing a crystallized semiconductor film without giving thermal damage by laser beam to the plastic film, as a method of forming a semiconductor thin film on a plastic film, by forming an amorphous material film and an oxide insulative film in this order on a plastic film, applying a laser beam on the side of the oxide insulative film and melting to crystallize the amorphous material film near the boundary between the amorphous material film and the oxide insulative film. Further, Japanese Unexamined Patent Application No. Hei 5-326402 also describes a method of forming a polycrystal silicon by layer by forming a thermo-barrier layer to a plastic film, forming an amorphous silicon layer thereof and then applying a laser beam in order to eliminate the effect of heat by the laser beam.
Each of the methods described above is a method of annealing the amorphous semiconductor film with a laser beam thereby crystallizing the same but this is a method of melting to crystallize only the surface of the amorphous semiconductor layer, or disposing a thermo-barrier layer such that the effect heat by the laser beam (which may possibly rise to 1000xc2x0 C.). Accordingly, the methods described above cannot crystallize the entire amorphous layer. Further, they require another step of providing the thermobarrier layer and also requires an expensive laser beam irradiation device. In addition, since it is necessary to scan the laser beam spot over the entire film, they also involve a disadvantage that it is difficult to increase the area of the film and take a long time for crystallizing the entire area.
Further, Japanese Published Unexamined Patent Application No. 2000-68520 describes a method of applying a VU-ray laser beam at a short wavelength (excimer laser beam) for converting an amorphous silicon thin film into a crystalline silicon semiconductor thin film. While this method gives less thermal effect to the base material, the base material is still heated to a temperature near 600xc2x0 C., so that only glass is used as the base material.
This invention has been accomplished in view of the problems described above and provides a method of manufacturing a semiconductor thin film which can be manufactured at a low temperature by using simple and convenient step and device, as well as to provide a substrate having a semiconductor thin film provided on a base material, a color filter forming substrate and a color filter using the substrate described above.
This can be attained by the provision of a method of manufacturing a semiconductor thin film, a substrate and a color filter described below.
According to an aspect of the present invention, a method of forming a crystalline semiconductor thin film on a base material has a step of: applying UV-rays to an amorphous semiconductor thin film provided on a base material while keeping a temperature at not less than 25xc2x0 C. and not more than 300xc2x0 C. in a vacuum or a reducing gas atmosphere.
The reducing gas atmosphere may contain a hydrogen gas.
The UV-rays may be light from an excimer lamp.
The kept temperature may be within a temperature range from 50xc2x0 C. to 250xc2x0 C.
The base material may be a plastic base material and the kept temperature may be within a temperature range from 50xc2x0 C. to the heat resistant temperature of the plastic base material. The heat resistant temperature of the plastic base material may be from 100 to 230xc2x0 C.
The amorphous semiconductor thin film may be an oxide semiconductor thin film.
The amorphous semiconductor thin film may be a titanium dioxide thin film formed by a sputtering method.
The crystalline semiconductor thin film may be an anatase type titanium oxide thin film or a thin film including mixed crystals of anatase type titanium dioxide and rutile type titanium dioxide.
A transparent conductive thin film may be disposed between the base material and the amorphous semiconductor thin film.
Another aspect of the present invention provides a lamination having at least a base material and a crystalline semiconductor thin film manufactured by the method described above.
Another aspect of the present invention also provides a lamination having at least a base material, a transparent conductive thin film and the crystalline semiconductor thin film manufactured by the described above.
The base material may be a plastic base material.
The lamination may be used as a substrate for forming a color filter.
Another aspect of the present invention also provides a lamination at least having a plastic base material and a crystalline semiconductor thin film.
The crystalline semiconductor thin film may be an anatase type titanium oxide thin film or a thin film comprising mixed crystals of anatase type titanium dioxide and rutile type titanium dioxide.
Another aspect of the present invention also provides a lamination having at least a plastic base material, a transparent conductive thin film and a crystalline semiconductor thin film in this order.
The lamination may be used as a substrate for forming a color filter.
Another aspect of the present invention provides a color filter having the lamination described above and a colored film formed on the lamination by a photo-electrodeposition method or a photocatalytic method.
Another aspect of the present invention also provides a method of applying UV-rays to an amorphous metal oxide thin film disposed on a base material under a reduced pressure or in a reducing gas atmosphere, thereby changing the amorphous metal oxide into a crystalline metal oxide thin film.
UV-rays may be irradiated uniformly on the thin film.
The method may further include a step of keeping a temperature higher than a normal temperature during irradiation of the UV-rays.